There are of course some caveats, aren’t there always caveats!. You can only stack specific switches with themselves. For instance you can only stack a Nortel Ethernet Routing Switch 5500 series switch (5510, 5520, 5530) with anther Nortel Ethernet Routing Switch 5500 series. You can’t stack a Nortel Ethernet Routing Switch 4500 series with a Nortel Ethernet Routing Switch 5500 series. The stack cables are very different so it shouldn’t be too hard to figure out. The switches must have the same software version of code on them in order to stack properly. The newer Ethernet Routing Switch 4500/5500 series switches will try to automatically upgrade any switch that is added to the stack and isn’t running the appropriate software version.

You can cascade/stack older Ethernet Switch 450, Ethernet Switch 460 and Ethernet Switch 470 switches. I would not advise stacking the Ethernet Switch 450 with either the ES460 or ES470 even though Nortel claims you can. There’s no issue stacking a Nortel Ethernet Switch 460 with the Ethernet Switch 470.

Cheers!

Let me start by telling you (if you don’t know already) that you can’t stack Ethernet Switch 460/470s with the Ethernet Routing Switch 5500. You also can’t use the Ethernet Switch 460/470 cascade cables with the Ethernet Routing Switch 5500 series switches.

The Ethernet Routing Switch 5500 series has the same basic LEDs as the Ethernet Switch 470, Up, Down, Base, etc. A green light indicates that everything is good while an amber or no light indicates a problem. I’ve found the Ethernet Routing Switch 5500 series to be much easier switch to stack for a number of reasons. One long overdue feature that is now available in the ERS 5500 series is automatic firmware/software upgrade. You can add a switch to the stack and the base unit will automatically push the running firmware/software to the recently added switch. You may need to be running at least v4.2 software for this to work although I’ve been unable to confirm as of yet.

Another feature is the ability to run loopback testing of the cascade/stack ports while the switch is running the agent software, there’s no need to reboot the switch and start the diagnostic code. You can also physically test the cable by looping it between the up and down stack ports (on the same switch) and the LEDs for both ports (Up and Down) should turn amber. If they both don’t turn amber you’ve got a problem somewhere, either with the cable or with the cascade module in the switch itself.

I should note that there was also a recall by Nortel on various cascade cables manufactured in 2005. If you have any cascade cables that have an “/05” designation on them you might want to contact Nortel to see if those cables were recalled. As a side note to that I recently discovered 7 cables out of 10 that were defective out of the box. They had the manufactured date of “11212007” on the bag.

5520-48T-PWR#stack loopback-test internal
Testing uplink port ... Ok
Testing downlink port ... Ok
Internal loopback test PASSED

5520-48T-PWR#stack loopback-test external
External loopback test PASSED.

Cheers!

Let me describe a typical scenario and then offer some ways of isolating the potential problem. You have a stack of four ES470s we’ll refer to as Unit 1, Unit 2, Unit 3 and Unit 4. We can use the picture to the left to visualize what a stack of four Ethernet Switch 470s might look like. While all the Up/Down stack lights should be green let’s just say that Unit 3 Down and Unit 4 Up is amber.

Let me just warn you that I have yet to figure how to truly identify a bad cascade module (the module that is built into the switch) from a bad cable without using either a cascade module that is know to be good and/or cascade cable that is know to be good in a process of elimination.

How you can determine if you have a bad cascade cable or cascade module?

It’s really pretty easy although it will require you to take the switch down and use the diagnostic boot code. You’ll need to cable up to the serial interface of the switch in order to run the test. When you’re ready go ahead and cold boot the switch. When you see the following, “470-24T  Diagnostics 3.6.0.7” (or something similar since you may not have a 24T but a 48T) you’ll need to interrupt the boot sequence by hitting Ctrl-C (go ahead and hit it repeatedly). You should see something similar to the following;

470-24T  Diagnostics 3.6.0.7

Testing main memory - PASSED

>> Break Recognized - Wait..

>> Break Recognized - Wait..

Press 'a'  to run Agent code
Press 'c'  to run Cascade external loopback test
Press 'd'  to Download agent code
Press 'e'  to display Errors
Press 'i'  to Initialize config/log flash
Press 'p'  to run POST tests
Press 'r'  to Receive cascade test packets
Press 's'  to Send    cascade test packets..

Once your at this point you’ll need to take a single cascade cable and loop it between the Up and Down port of the switch your working on. This will put a physical loop between the two interfaces so we can run and external loopback test across the cascade links. When you’re ready go ahead and select “c” from the diagnostics menu.

Test 501  Stack External Loopback    -        FAILED
NSX SXLB STAK: Stack Upstream Clock Failed. UCR=27 DCR=A7

In my case the Ethernet Switch 470 24 Port switch that I was using failed the loopback test. I then took a cascade cable that I knew to be working and repeated the test. It subsequently failed again which indicates to me that the cascade module is faulty. If you were to select “e” from the diagnostics menu you might seem something similar to the following;

System Resets  =       58.

Burn-In Loops  =        0.
Burn-In Errors =        0.
Auto-Burn-In   = DISABLED
Diag Baud      =     9600.

Error Log:
Bad Port Mask  = 80000000
Loop Test Error Description:
  50  501 STAK: Stack Secondary Rx (1) Timed Out
  50  501 STAK: Stack Upstream Clock Failed. Is Cascade Cable Missing?
  50  501 STAK: Stack Secondary Rx (1) Timed Out
  50  501 STAK: Stack Secondary Rx (1) Timed Out
  50  501 STAK: Force Stack RNGO Low Failed Test=0 GCReg=60
  50  501 STAK: Force Stack RNGO Low Failed Test=0 GCReg=60
  56  501 STAK: Stack Upstream Clock Failed. UCR=27 DCR=A7
  56  501 STAK: Stack Upstream Clock Failed. UCR=27 DCR=A7
  58  501 STAK: Stack Upstream Clock Failed. UCR=27 DCR=A7

One very important note! You can only stack switches that are running the same version of software (boot code and agent code). I believe the “Base” light will blink amber if you try to stack two switches together that are not running the same software.

You can also confirm a cascade/stacking issue remotely using Nortel’s Device Manager. Here’s a screenshot of two Ethernet Switch 470s stack together. You can see the yellow LEDs on Unit 1 Up and Unit 2 Down.

I will let you know that we’ve had our own share of cascade modules go bad over the past five years. While the cascade modules appear to be “replaceable” they really not designed to be field serviceable. If a switch fails the cascade loopback test it’s really only good for stand alone operation.

Cheers!